Tomographic Velocity Estimation in the Presence of Low Velocity Zones

摘要

A typical seismic crosshole geometry was studied using a tomographic approach in order to estimate velocities in the crosshole area. Methods to eliminate errors resulting from decomposition into a small number of cells are outlined. It is demonstrated that errors in travel time measurements can be large. An iterative procedure to account for ray bending effects is proposed. A heuristic approach was tested. Synthetic examples indicate how errors distort the solution.